JP2022121212A - Motorcycle tire - Google Patents

Abstract

To provide a motorcycle tire which improves rim slippage prevention performance and operation stability while keeping rim assembling performance.SOLUTION: A motorcycle tire comprises: a pair of bead parts 4 in which bead cores 5 are respectively embedded. The pair of bead parts 4 include a rim contact surface 10. The rim contact surface 10 includes a bead bottom surface 11, a bead side surface 12, and a bead heel surface 13. In a virtually rim-assembled state, diameter of intersection between a virtual first straight line 16 in which the bead bottom surface 11 is extended in the tire axial direction outer side and a virtual second straight line 17 in which the bead side surface 12 is extended in the tire radial direction inner side is 99.0%-99.6% of the rim diameter of a normal rim R.SELECTED DRAWING: Figure 2

Description

The present invention relates to tires for motorcycles.

For example, Patent Literature 1 below proposes a motorcycle tire in which fitability with a rim and steering stability performance are improved in a well-balanced manner by specifying the angle of the bead bottom surface of the bead portion with respect to the tire axial direction. there is

JP 2018-79802 A

In recent years, there has been a demand for further improvement in steering stability of tires for motorcycles. One of the means for improving the steering stability is to improve the rim displacement prevention performance of a motorcycle tire. However, increasing the rim deviation prevention performance tends to lead to deterioration of the rim assembly performance.

The present invention has been devised in view of the actual situation as described above, and the main object of the present invention is to provide a motorcycle tire that maintains rim assembly performance while improving rim displacement prevention performance and steering stability. there is

The present invention provides a motorcycle tire comprising a pair of bead portions each having a bead core embedded therein, the pair of bead portions being mounted on a normal rim and adjusted to a normal internal pressure. The rim contact surface includes a bead bottom surface extending in the tire axial direction inside the bead core in the tire radial direction and extending in the tire radial direction outside the bead core in the tire axial direction. It includes a bead side surface and an arc-shaped bead heel surface that connects the bead bottom surface and the bead side surface, and is not attached to the rim, and the bead side surfaces of the pair of bead portions are held at the rim width of the regular rim. In the virtual rim assembled state, the diameter of the intersection of a virtual first straight line extending the bead bottom surface axially outward and a virtual second straight line extending the bead side surface radially inward is It is 99.0% to 99.6% of the rim diameter of the regular rim.

In the motorcycle tire of the present invention, the bead bottom surface is continuous with the first bottom surface to the inner side of the first bottom surface in the tire axial direction, and extends at an angle larger than that of the first bottom surface with respect to the tire axial direction. It preferably includes two bottom surfaces.

In the motorcycle tire of the present invention, it is preferable that the angle of the first bottom surface with respect to the axial direction of the tire is 7° or less.

In the motorcycle tire of the present invention, it is preferable that the angle of the second bottom surface with respect to the axial direction of the tire is 24° or less.

In the motorcycle tire of the present invention, it is preferable that the thickness of the rubber on the outer side of the bead core in the axial direction is 3.0 mm or less at the center of the bead core in the tire radial direction.

Employing the above configuration, the motorcycle tire of the present invention can improve rim deviation prevention performance and steering stability while maintaining rim assembly performance.

1 is a cross-sectional view showing an embodiment of a motorcycle tire of the present invention; FIG. FIG. 2 is an enlarged view of the bead portion of FIG. 1;

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a tire meridional cross-sectional view including a tire rotation axis of a motorcycle tire 1 (hereinafter, sometimes simply referred to as "tire") according to the present embodiment in a normal rim mounted state. The tire 1 of this embodiment is a tire for the front wheel of a motorcycle suitable for on-road sports driving. However, the tire of the present invention is not limited to such an aspect.

"Regular rim mounting state" means a state in which the tire is mounted on a normal rim R and adjusted to a normal internal pressure. In this specification, unless otherwise specified, the dimensions of each portion of the tire are values measured with the normal rim mounted.

"Regular rim R" is a rim defined for each tire in a standard system including standards on which tires are based. For example, "standard rim" for JATMA and "design rim" for TRA , ETRTO is "Measuring Rim". In the case of a tire for which no standard has been established, a rim that allows the performance of the tire to be fully exhibited is used as the regular rim, for example, a rim recommended by the manufacturer.

"Regular internal pressure" is the air pressure specified for each tire by each standard in the standard system including the standards on which tires are based. Maximum value described in VARIOUS COLD INFLATION PRESSURES", or "INFLATION PRESSURE" for ETRTO. In the case of a tire for which no standard has been established, the regular internal pressure is the internal pressure that allows the performance of the tire to be fully exhibited, for example, the internal pressure recommended by the manufacturer.

As shown in FIG. 1 , the tire 1 of this embodiment includes a tread portion 2 , a pair of sidewall portions 3 and a pair of bead portions 4 . The sidewall portions 3 are continuous on both sides of the tread portion 2 in the tire axial direction. The bead portion 4 continues to the inner side of the sidewall portion 3 in the tire radial direction. In the tread portion 2, the ground contact surface between one tread end Te and the other tread end Te is convex outward in the tire radial direction so that a sufficient ground contact area can be obtained even during cornering with a large camber angle. curved in an arc. A bead core 5 is embedded in the bead portion 4 .

The tire 1 of this embodiment includes a carcass 6 extending from one bead portion 4 to the other bead portion 4 via one sidewall portion 3 , the tread portion 2 , and the other sidewall portion 3 .

Carcass 6 includes, for example, carcass ply 6A including a plurality of carcass cords. The carcass 6 of the present embodiment is composed of one carcass ply 6A, but may be composed of a plurality of carcass plies. The carcass ply 6A includes a main body portion 6a and a folded portion 6b. The body portion 6a extends from the tread portion 2 to the bead cores 5 of the bead portions 4 on both sides through the sidewall portions 3 on both sides. The folded portion 6b continues to the main body portion 6a and folds around the bead core 5 from the inner side to the outer side in the axial direction of the tire.

The tread portion 2 is provided with, for example, a belt layer 7 and a band layer 8 . The belt layer 7 includes, for example, a belt ply including a plurality of belt cords inclined at 10 to 45° with respect to the tire circumferential direction. Although the belt layer 7 of this embodiment is composed of one belt ply, it may be composed of a plurality of belt plies. The band layer 8 includes, for example, a jointless band ply in which a band cord is spirally wound at an angle of 5° or less with respect to the tire circumferential direction. Such belt layer 7 and band layer 8 can effectively reinforce the tread portion 2 .

The pair of bead portions 4 includes rim contact surfaces 10 that come into contact with the regular rim R in the regular rim mounted state.

An enlarged view of the bead portion 4 is shown in FIG. As shown in FIG. 2 , rim contacting surface 10 includes bead bottom surface 11 , bead side surface 12 and bead heel surface 13 . The bead bottom surface 11 extends in the tire axial direction inside the bead core 5 in the tire radial direction. The bead side surface 12 extends radially outward of the bead core 5 in the axial direction of the tire. The bead heel surface 13 is formed of an arcuate outer surface that connects the bead bottom surface 11 and the bead side surface 12 .

In the present invention, the bead bottom surface 11 is extended outward in the tire axial direction in a virtual rim assembled state in which the bead side surfaces 12 of the pair of bead portions 4 are held at the rim width of the regular rim R in a non-mounted state on the rim. The diameter D2 of the intersection point 20 between the imaginary first straight line 16 and the imaginary second straight line 17 extending radially inward from the bead side surface 12 is 99% of the rim diameter D1 of the regular rim R (shown in FIG. 1). .0% to 99.6%. The first straight line 16 corresponds to a tangent line passing through the end of the bead bottom surface 11 on the bead heel surface 13 side, and the second straight line 17 corresponds to a tangent line passing through the end of the bead side surface 12 on the bead heel surface 13 side. The diameter D2 corresponds to the diameter of an imaginary circle formed when the points of intersection 20 of the first straight lines 16 and the second straight lines 17 are brought together over the entire circumference of the tire.

In the present invention, by adopting the above configuration, it is possible to improve the rim deviation prevention performance and the steering stability while maintaining the rim assembly performance. The reason for this is presumed to be the following mechanism.

As a result of various experiments, the inventors have found that the rim assembly performance depends not only on the size of the diameter of the bead baseline BL, but also on the size of the angle of the bead side surface 12 with respect to the tire radial direction. This is because when the bead portion 4 rides over the hump of the rim, the larger the angle of the bead side surface, the easier it is for the inner diameter of the tire to expand when the rim is pressed against the bead portion 4, thereby improving the rim assembly performance. Conceivable.

Further, the inventors have found that the rim deviation prevention performance depends not only on the size of the diameter of the bead baseline BL, but also on the size of the angle of the bead bottom surface 11 with respect to the tire axial direction. This is thought to be because the larger the angle of the bead bottom surface 11 is, the more strongly the bead portion 4 is pressed against the rim when the rim is assembled, thereby improving the rim displacement prevention performance.

As a result of further research, in order to achieve both rim assembly performance and rim deviation prevention performance, the diameter D2 of the intersection point 20 of the first straight line 16 and the second straight line 17 should be set to an appropriate angle between the bead side surface 12 and the bead bottom surface 11. It turned out to be vital to be specific. In the present invention, by specifying the diameter D2 to be 99.0% to 99.6% of the rim diameter D1 of the regular rim, it is possible to improve the rim deviation prevention performance while maintaining the rim assembly performance. In addition, it is thought that the steering stability is also improved because the driver's operation is accurately transmitted to the tire by improving the rim deviation prevention performance.

A more detailed configuration of the present embodiment will be described below. Each configuration described below represents a specific aspect of the present embodiment. Therefore, it goes without saying that the present invention can exhibit the above effects even if it does not have the configuration described below. Further, even if any one of the configurations described below is applied singly to the tire of the present invention having the features described above, it is possible to expect an improvement in performance according to each configuration. Furthermore, when some of the respective configurations described below are applied in combination, it is possible to expect a combined improvement in performance according to each configuration. It should be noted that the configuration of the present embodiment described below was measured under the virtual rim assembly state described above, unless otherwise specified.

In a preferred embodiment, the diameter D2 is 99.3% to 99.5% of the rim diameter D1 of the regular rim R. Also, the angle θ1 between the first straight line 16 and the second straight line 17 is, for example, 90 to 110°, preferably 95 to 105°.

The bead core 5 of this embodiment has a rectangular cross-sectional shape surrounded by two first side surfaces 5a and two second side surfaces 5b in the tire cross section. However, the corner portion where the first side surface 5a and the second side surface 5b continue is curved in an arc shape. The two first side surfaces 5a each extend along the tire axial direction. The two second side surfaces 5b each extend along the tire radial direction. The angle difference between the two second side surfaces 5b is, for example, 10° or less, preferably 5° or less. In a more desirable embodiment, the two second side surfaces 5b extend substantially parallel. Such a bead core 5 reliably prevents the bead portion 4 from collapsing, and serves to enhance steering stability.

The bead bottom surface 11 is connected to a first bottom surface 21 that is inclined with respect to the tire axial direction, and a first bottom surface 21 that extends axially inward of the first bottom surface 21 and extends at an angle larger than that of the first bottom surface 21 with respect to the tire axial direction. and two bottom surfaces 22 . The bead bottom surface 11 including the first bottom surface 21 and the second bottom surface 22 improves rim assembly performance and rim deviation prevention performance in a well-balanced manner.

The first bottom surface 21 of the present embodiment extends linearly in the cross section of the tire in the virtual rim assembled state. The angle of the first bottom surface 21 with respect to the axial direction of the tire is, for example, 15° or less, preferably 10° or less, and more preferably 7° or less. Specifically, the angle of the first bottom surface 21 is 3 to 7 degrees. More preferably, the angle between the first bottom surface 21 and the first side surface 5a of the bead core 5 is 0-10°. In this embodiment, the angle of the first bottom surface 21 matches the angle of the first straight line 16 with respect to the axial direction of the tire.

The second bottom surface 22 of the present embodiment extends linearly in the cross section of the tire in the virtual rim assembled state. The angle of the second bottom surface 22 with respect to the axial direction of the tire is, for example, 30° or less, preferably 24° or less. Specifically, the angle of the second bottom surface 22 is 18 to 24 degrees. Such a second bottom surface 22 can improve rim deviation prevention performance while maintaining rim assembly performance.

The angle θ2 between the first bottom surface 21 and the second bottom surface 22 is preferably 150° or more, more preferably 160° or less, in order to improve the rim assembly performance and the rim deviation prevention performance in a well-balanced manner. is 175° or less, more preferably 170° or less.

The angle θ2 between the first bottom surface 21 and the second bottom surface 22 is larger than the angle θ1 between the first straight line 16 and the second straight line 17 . The difference between the angle θ1 and the angle θ2 is, for example, 60-80°, preferably 65-75°. As a result, the pressure of the bead side surface 12 acting on the rim and the pressure of the second bottom surface 22 acting on the rim are improved in a well-balanced manner, thereby exhibiting excellent steering stability.

In the tire cross section, a boundary 25 between the first bottom surface 21 and the second bottom surface 22 is arranged, for example, in a region obtained by virtually extending the bead core 5 inward in the tire radial direction. Moreover, the boundary 25 is desirably located axially inward of the center position of the bead core 5 in the axial direction of the tire. The axial distance between the boundary 25 and the center position of the bead core 5 is, for example, 25% to 35% of the axial width of the bead core 5 . As a result, the second bottom surface 22 can be firmly adhered to the rim, and the durability of the bead portion 4 is improved.

The bead side surface 12 includes a portion extending linearly from the end on the bead heel surface 13 side in the tire cross section. This portion has an angular difference of, for example, 5° or less with respect to the second side surface 5b of the bead core 5 .

At the tire radial position at the center of the bead core 5 in the tire radial direction, it is desirable that the thickness of the rubber on the axially outer side of the bead core 5 is 3.0 mm or less. This makes it easier for the bead portion 4 to climb over the hump, further improving the rim assembly performance.

Although the motorcycle tire according to one embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above, and can be implemented in various modifications.

A motorcycle tire (front wheel tire) of size 120/70ZR17 having the basic structure shown in FIG. 1 was manufactured based on the specifications shown in Tables 1 and 2. Further, as Comparative Examples 1 and 2, prototype tires were produced in which the diameter at the intersection of the first straight line and the second straight line was out of the scope of the present invention. The tires of Comparative Examples 1 and 2 have substantially the same configuration as the tires of the Examples, except for the matters described above. Each test tire was tested for rim assembly performance, rim deviation prevention performance, and steering stability. Common specifications and test methods for each test tire are as follows.
Rim size: MT3.50
Tire pressure: 250kPa
Test vehicle: Displacement 1000cc

<Rim assembly performance>
The maximum internal pressure was measured when the bead portion of the tire climbed over the hump of the rim when the tire was internally pressure-filled when the tire was mounted on the rim. The result is the reciprocal of the maximum internal pressure, and is indicated by an index with Comparative Example 1 being 100. The larger the numerical value, the smaller the maximum internal pressure and the better the rim assembly performance.

<Rim misalignment prevention performance>
In accordance with JIS-D4230, a load was applied from the lateral direction to the bead portion of a tire assembled with a rim and not filled with internal pressure, and the resistance was measured when the bead portion was separated from the rim. The results are shown as an index with the resistance of Comparative Example 1 being 100, and the larger the number, the better the rim assembly performance.

<Steering stability>
The steering stability was evaluated by the driver's sensory perception when the test vehicle equipped with the test tires was run on a circuit. The results are scored with Comparative Example 1 being 100, and the larger the number, the better the steering stability.
The results of the tests are shown in Tables 1-2.

As a result of the test, it was confirmed that the tire of the example improved the rim deviation prevention performance and the steering stability while maintaining the rim assembly performance.

4 bead portion 5 bead core 10 rim contact surface 11 bead bottom surface 12 bead side surface 13 bead heel surface 16 first straight line 17 second straight line R regular rim

Claims (5)

A tire for a motorcycle,
including a pair of bead portions each having a bead core embedded therein;
The pair of bead portions includes a rim contact surface that is attached to a regular rim and contacts the regular rim in a regular rim mounted state adjusted to a regular internal pressure,
The rim contact surface connects a bead bottom surface extending in the tire axial direction inside the bead core in the tire radial direction, a bead side surface extending in the tire radial direction outside the bead core in the tire axial direction, and the bead bottom surface and the bead side surface. an arcuate bead heel surface;
In a virtual rim assembled state in which the bead side surfaces of the pair of bead portions are held at the rim width of the regular rim,
The diameter of the point of intersection between a first imaginary straight line extending axially outward from the bottom surface of the bead and a second imaginary straight line extending radially inward from the side surface of the bead is 99% of the rim diameter of the regular rim. 0% to 99.6%;
Motorcycle tires. 2. The bead bottom surface includes a first bottom surface and a second bottom surface that extends axially inward of the first bottom surface and extends at an angle greater than that of the first bottom surface with respect to the tire axial direction. The motorcycle tire described in . The motorcycle tire according to claim 2, wherein the angle of the first bottom surface with respect to the axial direction of the tire is 7° or less. The motorcycle tire according to claim 2 or 3, wherein the second bottom surface has an angle of 24° or less with respect to the axial direction of the tire. 5. The motorcycle according to any one of claims 1 to 4, wherein the rubber thickness of said bead core on the outer side in the tire axial direction is 3.0 mm or less at a position in the tire radial direction at the center of said bead core in the tire radial direction. for tires.

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